In recent years, as a refining method for recovering nickel and cobalt from nickel oxide ores containing nickel and cobalt respectively about 1.0 to 2.0% and about 0.1 to 0.5% relative to the total amounts thereof, a high-temperature pressure acid leaching method (hereinafter, referred to sometimes as HPAL Method: high pressure acid leach), which is one of wet refining methods, has been utilized.
The HPAL method is a leaching treatment method in which, for example, sulfuric acid is added to an ore slurry of nickel oxide ores, and a leaching process is carried out under high-temperature and high-pressure so that a leached liquor containing nickel and cobalt is obtained. In this case, a refining method is carried out in which the leaching step utilizing the HPAL method, a neutralizing step of adjusting the pH of the resulting leached liquor and of forming a neutralized deposit slurry containing impurities such as iron or the like and a mother liquor for use in nickel recovery, which is purified, and a sulfidizing step of supplying a hydrogen sulfide gas to the nickel recovery-use mother liquor so as to form a nickel-cobalt mixed sulfide and a barren liquor are carried out (for example, see Patent Document 1).
In this refining method, in the leaching step, in general, nickel and cobalt of 90% or more contained in the ore slurry are leached out. Then, after the separation of the leached liquor, impurities in the leached liquor are separated and removed therefrom by a neutralizing method so that a nickel-cobalt mixed sulfide having a nickel quality of 55 to 60% and a cobalt quality of about 3 to 6% can be obtained, and this is used as an intermediate material for use in the nickel-cobalt refining process.
In this case, raw material ores, such as nickel oxide ores, to be used in the above-mentioned refining process or the like are normally subjected to an ore treatment and processed into an ore slurry so as to be loaded into a refining process, and they are used in a leaching treatment, etc., in the form of the ore slurry.
More specifically, the ore treatment for the raw material ores is mainly classified into a pulverizing/classifying step in which the raw material ores are subjected to a pulverizing process and a classifying (sieving) process including multiple stages and an ore slurry condensing step in which ore components are condensed.
First, in the pulverizing/classifying step, a pulverizing process for the raw material ores by the use of a wet facility and a classifying process for removing oversized ore particles and mixed matters are carried out so that a coarse ore slurry composed of undersized ore particles is produced (for example, see Patent Document 2).
In this case, since the produced coarse ore slurry contains excessive moisture, the excessively contained moisture is removed in the next ore slurry condensing step (for example, see Patent Document 3). Since the ore components contained in the ore slurry per the same transporting amount are increased, this moisture removal is effective for improving the operation efficiency of the plants as a whole.
However, the above-mentioned conventional ore treatment tends to form fine ore particles due to fluctuations of the grain size of the raw material ores to be loaded and degrees of pulverization in the pulverizing process, with the result that the viscosity of the resulting ore slurry tends to become too high.
More specifically, upon adjusting the ores to a predetermined grain size by the pulverizing process and the classifying (sieving) process including multiple steps, fine ore particles are formed, with the result that the grain size of the undersized ore particles that have been classified and recovered tends to be shifted to a small size. In this case, even after the pulverizing/classifying step, since no process for removing fine ore particles is prepared, an ore slurry having a small grain size tends to be obtained. It has been known that when such an ore slurry is used, the viscosity of the ore slurry becomes too high.
Additionally, in the case when the viscosity of an ore slurry is represented at the actual operation site, a value (unit: Pa) of a yield stress is generally used as an alternative index. The reason for this is because the yield stress is more easily measured, and because as the viscosity of the ore slurry becomes higher, the value of the yield stress also becomes greater, while, in contrast, as the viscosity becomes lower, the value of the yield stress also becomes smaller, so that an erroneous recognition hardly occurs. Therefore, in the following description, the yield stress of the ore slurry is sometimes used for indicating the viscosity of the ore slurry.
On the other hand, the capability of a transporting pump for use in transporting the ore slurry to a metal refining process, such as a leaching step or the like, is generally set to 200 Pa or less in the yield stress of the ore slurry; thus, a reasonable facility price is obtained, with a comparatively simple structure.
Therefore, in the case when the yield stress of the ore slurry becomes high as described above, and exceeds, for example, 200 Pa, a problem is raised in that the transporting process cannot be carried out by using a general-use slurry transporting pump. Such a problem causes a situation in which the plant has to be temporarily stopped, resulting in a serious reduction in operation efficiency.
In order to prevent such a viscosity rise in the ore slurry, a method is proposed in which “a shearing pump” that utilizes an effect for reducing the viscosity in the slurry (Shear Thinning effect), by applying a shearing force thereto several times prior to transporting the slurry; however, this method undesirably requires expensive facilities, and causes a complicated facility structure, and high costs for introducing the method as well as high maintenance costs.
Moreover, in the case when such an ore slurry with high viscosity is transported to the leaching process using, for example, the HPAL method, although the ore slurry can be transported by using the above-mentioned shearing pump, upon providing a high-temperature state by heat exchange with high-temperature water vapor by using a heat exchanger in the initial stage of the leaching process, the heat exchanging efficiency is lowered. This is because when the yield stress of the ore slurry becomes such a high degree as to exceed, for example, 200 Pa, in the initial stage after being loaded into a heat exchanger, the ore slurry tends to adhere to its wall surfaces and members, and anchored thereon without being allowed to flow, resulting in clogging of the device in the worst case.
On the other hand, for example, in order to avoid the grain size of the ores to be loaded from becoming too small, a method is easily proposed in which a process for removing fine ore particles is newly installed as the final stage of the pulverizing/ classifying step; however, high costs are required for introducing such a facility. Moreover, the amount of ores to be rejected from the pulverizing/classifying step increases to cause a problem in that resources are not effectively utilized.
Moreover, as the viscosity adjusting method, for example, as described in Patent Document 4, a method or the like is proposed in which in order to allow muddy water whose viscosity is unknown to exert a predetermined viscosity, the added water amount is adjusted; however, this technique relates to an adjusting method for the viscosity of muddy water for use in a shield engineering technique, a pile engineering technique, a fluidization treatment engineering technique, an underground continuous wall engineering technique and the like in the construction field, and it is difficult to apply this method to the viscosity adjusting method for an ore slurry after having been dehydrated.